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Chapter 39Major

Ecosystems of the Biosphere

On Land, the Biosphere Is Organized into

Terrestrial Ecosystems

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39.1 Major terrestrial ecosystems are characterized

by particular climates

Each major terrestrial ecosystem has a particular mix of plants and animals that are adapted to living under certain conditions, particularly climate Climate - average yearly temperature and

precipitation of a region When terrestrial ecosystems are plotted

according to their climate, a particular distribution pattern results

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Figure 39.1 Pattern of ecosystem distribution on land

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39.2 The tundra is cold and dark much of the year

Arctic tundra encircles the Earth just south of the ice-covered polar seas in the Northern Hemisphere Covers about 20% of the Earth’s land surface

Arctic tundra is cold and dark much of the year Its winters are extremely long, cold, and harsh, and its summers

are short (6–8 weeks) Because rainfall amounts to only about 20 cm a year, the

tundra could possibly be considered a desert Only the topmost layer of soil thaws, permafrost beneath this

layer is always frozen Trees are not found in the tundra

Growing season too short and roots cannot penetrate permafrost

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Figure 39.2 Tundra, the northern-most ecosystem

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39.3 Coniferous forests are dominated by gymnosperms

Coniferous forests are found in three locations Taiga - which extends around the world in the northern part of

North America and Eurasia Near mountaintops (called montane coniferous forest) Along the Pacific coast of North America, as far south as

northern California Taiga (called boreal or northern) forest, exists south of

the tundra and covers approximately 11% of the Earth’s landmasses Needlelike leaves of its cone-bearing trees can withstand the

weight of heavy snow Temperate rain forest - coniferous forest that runs

along the west coasts of Canada and the United States Plentiful rainfall and rich soil produce some of tallest trees ever Also called old-growth because some trees are >1,000 years old

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Figure 39.3 Taiga, a northern coniferous forest

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39.4 Temperate deciduous forests have abundant life

Temperate deciduous forests Found south of the taiga in eastern North America, eastern

Asia, and much of Europe Seasons are well defined, and growing season ranges

between 140 and 300 days Trees (oak, beech, sycamore, and maple) have broad leaves

and are deciduous - lose their leaves in fall and grow them in spring

Tallest trees form a canopy, but enough sunlight penetrates to provide energy for understory trees Stratification provides habitats for insects and birds

Autumn fruits, nuts, and berries provide food for the winter Leaves, after turning brilliant colors and falling to the ground,

contribute to a rich layer of humus39-10

Figure 39.4 Temperate deciduous forest in the fall

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39.5 Temperate grasslands have extreme seasons

Temperate grasslands Include Russian steppes, South American pampas,

and North American prairies Bitterly cold winters and hot and dry summers Across the United States from east to west

Temperate deciduous forest transitions into tall-grass prairie roughly along the border between Illinois and Indiana

Tall-grass prairie requires more rainfall than does the short-grass prairie, which occurs near desert

Large herds of bison (hundreds of thousands) once roamed the prairies, and pronghorn antelope

Small mammals, (mice, prairie dogs, and rabbits) live below ground, but usually feed aboveground

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Figure 39.5 Temperate grassland in the summer

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39.6 Savannas have wet-dry seasons

Savannas - in regions where a cool dry season is followed by hot rainy season Largest savannas are in central and southern Africa

Other savannas in Australia, Southeast Asia, and South America

Characterized by large expanses of grasses with sparse populations of trees Plants have extensive and deep root systems that enable

them to survive drought and fire African savanna supports the greatest variety and

number of large herbivores of all the biomes Elephants and giraffes are browsers that feed on tree

vegetation Antelopes, zebras, wildebeests, water buffalo, and some

rhinoceroses are grazers that feed on grasses39-14

Figure 39.6 The African savanna

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39.7 Deserts have very low annual rainfall

Deserts usually found at latitudes of about 30° in both the Northern and Southern Hemispheres Winds that descend in these regions lack moisture, and the

annual rainfall is less than 25 cm Days are hot because a lack of cloud cover allows the sun’s rays

to penetrate easily Nights are cold because heat escapes easily into atmosphere

Most have plants highly adapted to survive long droughts, extreme heat, and extreme cold

Thick epidermal layers, water-storing stems and leaves, and the ability to set seeds quickly in the spring

Sahara Desert and a few others have little vegetation Some animals are adapted to the desert environment

To conserve water, many desert animals are nocturnal or burrowing and have a protective outer body covering

A desert has numerous insects, which pass through the stages of development when there is rain

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Figure 39.7 Desert with some vegetation

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39.8 Tropical rain forests are warm with abundant rainfall

Tropical rain forests of South America, Africa, and the Indo-Malayan Temperature is always warm (20° to 25°C) Rainfall is plentiful (minimum of 190 cm/year)

May be the richest ecosystem Diversity of species is enormous

10 km2 area of tropical rain forest may contain 1,500 species of flowering plants Complex structure, with many levels of life, including the forest

floor, the understory, and the canopy Sunlight is filtered out by canopy, and plants of the forest floor,

such as ferns, are tolerant of minimal light Understory consists of shorter trees that receive some light and

bear epiphytes Epiphytes are plants that grow on other plants but usually have roots of their

own that absorb moisture and minerals leached from their hosts Some animals live on the forest floor, but most live in the trees

Insects are so abundant that majority of species have not been identified 39-18

Figure 39.8A Levels of life in a tropical rain forest

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Figure 39.8B Representative animals of the tropical rain forests of the world

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39.9 Solar radiation and winds influence climate

Sun’s rays are more direct at the equator and more spread out at the polar regions Tropics are warmer than temperate regions

Overall flows of warm and cold air are modified into three large circulation cells in each hemisphere Rising air flows toward the poles, but at about 30° north and south

latitude, it sinks toward the Earth’s surface and reheats Deserts of Africa, Australia, and the Americas occur at these

latitudes At Earth’s surface, air flows both poleward and equatorward At about 60° north and south latitude, the air rises and cools,

producing additional zones of high rainfall Besides affecting precipitation, the spinning of the Earth

also affects the direction of the winds Periods of calm, called the doldrums, occur at the equator

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Figure 39.9A Left: Distribution of sun’s rays as the Earth orbits the sun. Right: Distribution of solar energy as the Earth orbits the sun

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Figure 39.9B Wind circulation as air moves from the equator to the poles and back again

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39.10 Topography and other effects also influence climate

Topography - surface features of land Mountains are topographic features that affect climate, and

distribution of ecosystems Difference between the windward side and the leeward side can be

quite dramatic Example: Hawaiian Islands

Windward receives more than 750 cm of rain a year Leeward side, which is in a rain shadow, gets on the average only

50 cm of rain and is generally sunny

Nearby Bodies of Water Ocean temperature is more stable than landmasses Ocean water gains or loses heat more slowly than terrestrial

environments Monsoon climate - wet ocean winds blow onshore for almost

half the year

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Figure 39.10A Elevation affects the distribution of terrestrial ecosystems

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Figure 39.10B Formation of a rain shadow

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Fresh Water and Salt Water Are Organized into Aquatic Ecosystems

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39.11 Fresh water flows into salt water

Fresh water flows within streams and rivers and is contained, at least temporarily, in lakes and ponds Mountain streams have cold, clear water with waterfalls and

rapids Streams join to form a river that flows gently River meanders across broad valleys, and empties into ocean At its mouth, river divides into many muddy channels of a delta Salt marshes are extremely productive ecosystems

Wetlands (wet some part of year) directly absorb storm waters and also absorb overflows from lakes and rivers In this way, they protect farms, cities, and towns from the

devastating effects of floods Lakes are often classified by nutrient status

Oligotrophic lakes are nutrient-poor, having a small amount of organic matter and low productivity

Eutrophic lakes are nutrient-rich, having plentiful organic matter and high productivity 39-28

Figure 39.11A A freshwater and saltwater ecosystem

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Figure 39.11B Types of lakes

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39.12 Marine ecosystems include those of the coast and the ocean Coastal Ecosystems Border the Oceans

Salt marshes, discussed previously, and also mudflats and mangrove swamps are ecosystems that occur at a delta Mangrove swamps develop in subtropical and tropical zones,

while marshes and mudflats occur in temperate zones Estuary - partially enclosed body of water where fresh

water and sea water meet and mix as a river enters the ocean Organisms living in an estuary must be able to withstand

constant mixing of waters and rapid changes in salinity Nearly two-thirds of marine fishes and shellfish spawn and

develop in the protective and rich environment of estuaries Intertidal zone - lies between the high and low tide marks

Rocky shores and sandy shores are constantly bombarded by the sea as the tides roll in and out

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Figure 39.12A Coastal ecosystems

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Figure 39.12B Ocean ecosystems

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Oceans Shallow ocean waters (euphotic zone) contain a greater

concentration of organisms than the rest of the sea Phytoplankton (algae) is food not only for zooplankton (protozoans and

microscopic animals) but also for small fishes Coral reefs - areas of biological abundance just below the

surface in shallow, warm, tropical waters Chief constituents are stony corals, animals that have a calcium carbonate

(limestone) exoskeleton, and calcareous red and green algae Most of the ocean lies within the pelagic zone

Epipelagic zone lacks the inorganic nutrients of shallow waters, and therefore it does not have as high a concentration of phytoplankton

Animals in the deeper waters of the mesopelagic zone are carnivores, which are adapted to the absence of light,

Waters of the bathypelagic zone are in complete darkness except for an occasional flash of bioluminescent light

Abyssal plain - many invertebrates survive there by feeding on debris floating down from the mesopelagic zone

At hydrothermal vents, sea water percolates through cracks and is heated to about 350°C, causing sulfate to react with water and form hydrogen sulfide

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Figure 39.12C Ocean inhabitants in divisions of pelagic zone

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39.13 Ocean currents affect climates

Climate is driven by the sun, but the oceans play a major role in redistributing heat in the biosphere Air takes on the temperature of the water below, and warm

air moves from the equator to the poles The oceans make the winds blow

Because the ocean currents eventually strike land, they move in a circular path Clockwise in the Northern Hemisphere and

counterclockwise in the Southern Hemisphere As the currents flow, they take warm water from the

equator to the poles One such current, called the Gulf Stream, brings tropical

Caribbean water to the east coast of North America and the higher latitudes of western Europe

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Figure 39.13 Ocean currents

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Connecting the Concepts:Chapter 39

Earth’s diverse ecosystems have resulted from interactions between the biotic communities and the abiotic environment Organisms create chemical and physical conditions of streams, lakes,

and oceans Over geologic time, the biosphere has been changing constantly

Changes in the sun’s radiation output and in the tilt of the Earth’s axis have altered the pattern of solar energy reaching the Earth’s surface

Geologic processes have modified conditions for life Modern humans have transformed vast areas of many of the

terrestrial biomes into farmland, cities, highways, and other developments Through our use of resources and release of pollutants, we have now

become an agent of global importance We still depend on the biodiversity that exists in the Earth’s biomes, and

on the interactions of other organisms within the biosphere These interactions influence climate, patterns of nutrient cycling and

waste processing, and basic biological productivity The Earth’s biotic diversity also provides enjoyment and inspiration to

millions of people, who spend billions of dollars to visit coral reefs, deserts, rain forests, and even the Arctic tundra 39-38